The present invention relates to an injection molding process and an apparatus therefor, and more particularly, related to a process for injection-molding a composite rein composition composed of particles and a binder resin, and an injection-molding machine used therefor.
Conventionally, as an injection-molding process and apparatus of such a type, there are known those described in Japanese Patent Application Laid-Open (KOKAI) No. 9-295329(1997).
As shown in FIG. 11, an injection-molding machine of the prior art is constituted by a kneader 1 for kneading a mixed starting material to be kneaded, an injection device 2 for injection-molding the kneaded material, a reservoir device 3 for temporarily storing the kneaded material to be fed to the injection device 2, and a switching valve (directional control valve) 4 being switchable between one position where the kneaded material is fed to the reservoir device 3 and another position where the kneaded material is fed to the injection device 2.
The kneader 1 is constituted by a heating barrel 5, an extrusion screw 6 which is mounted in the barrel so as to be rotatably driven by, for example, an oil motor, and a hopper 7 for feeding a raw material to be kneaded, which is fitted onto an outside of the heating barrel.
The injection device 2 is constituted by a heating barrel 8, an injection screw 9 which is mounted in the barrel so as to be rotatably driven by, for example, an oil motor and reciprocatively moved by a piston, and an injection nozzle 10 which is provided at a distal end thereof. Upon metering, a metering space 11 is formed on the front side of the injection screw 9 in the heating barrel 8.
The reservoir device 3 is constituted by a reservoir chamber 12 in which an extrusion plunger 13 is accommodated so as to be reciprocatively driven by a piston in the vertical direction. When the extrusion plunger 13 is moved upward, a storage space 14 is formed in the reservoir chamber 12 underneath the extrusion plunger 13.
The switching valve 4 is of a rotary type and has a valve body through which a straight passage for the kneaded material is formed.
An outlet (or inlet) 16 of the reservoir device 3 and an inlet 17 of the switching valve 4 are connected with each other through a passage 18, and an outlet 19 of the switching valve 4 and an inlet 20 of the injection device 2 are connected with each other through a passage 21. Further, a discharge end of the kneader 1 is opened into the mid-position of the passage 18 such that the kneader 1 is inclined downwardly toward the passage 18.
When performing the injection molding process using the above injection molding machine, the switching valve 4 is held in the closed position as shown in FIG. 11 (refer to a broken line in FIG. 11), and the kneader 1 is operated, thereby introducing the kneaded material into the reservoir device 3 through the passage 18. At this time, the extrusion plunger 13 is caused to move upward by the pressure of the kneaded material introduced, so that the kneaded material is temporarily stored in the storage space 14 formed underneath the extrusion plunger 13.
Then, the switching valve 4 is opened, and after a predetermined period of time therefrom, the extrusion plunger 13 is moved downward, thereby forcing the kneaded material to discharge downward from the storage space 14. The discharged kneaded material is merged (jointed) with a kneaded material freshly supplied from the kneader 1. The jointed kneaded material is then fed to the injection screw 9 of the injection device 2 through the switching valve 4, and the injection screw 9 is retarded, thereby transferring the kneaded material into the metering space 11 thus formed on the front side of the injection screw 9 to store the material therein.
Subsequently, as shown in FIG. 12, the switching valve 4 is closed, and the injection screw 9 is stopped to rotate and is allowed to move forward, whereby the kneaded material is injected through the injection nozzle 10 to obtain an aimed injection-molded product.
During the above injection molding step, the kneader 1 supplies a fresh kneaded material into the reservoir device 3 through the passage 18. The extrusion plunger 13 is forced to move upward by the pressure of the kneaded material introduced, so that the kneaded material is temporarily stored in the storage space 14 formed underneath the extrusion plunger 13.
Thus, the injection molding machine is returned to the initial condition as shown in FIG. 11, and subsequently the above operations are repeated.
However, in the conventional injection molding machine and injection molding process, when the kneaded material is discharged from the storage space 14 of the reservoir device 3 by the extrusion plunger 13 and introduced into the injection device 2, the extrusion pressure exerted by the extrusion plunger 13 is transmitted through the passage 18 to the kneader 1. For this reason, when the extrusion pressure acts on the kneader 1, the torque of the extrusion screw 6 is temporarily increased, thereby failing to perform a stable kneading operation in the kneader 1.
Further, the extrusion pressure tends to cause a reverse flow of the kneaded material from the reservoir device 3 through the passage 18 into the kneader 1. In such a case, the kneaded materials having different heat histories are disadvantageously mixed together upon kneading.
Accordingly, in the conventional injection molding machines and processes, there arise problems such as non- uniform quality of obtained injection molded products due to such an unstable injection molding process.
As a result of the present inventors"" earnest studies for solving the above problems, it has been found that using an injection molding machine having a pair of reservoir devices for temporarily storing a kneaded material, by (a) kneading particles and a binder resin using a kneader, (b) feeding the obtained kneaded material to one (A) of the two reservoir devices, (c) feeding the kneaded material stored in the reservoir device (A) to an injection device, and simultaneously feeding the kneaded material from the kneader to another reservoir device (B) to store the material therein, (d) feeding the kneaded material stored in the reservoir device (B) to the injection device, and simultaneously feeding the kneaded material from the kneader to the said one reservoir device (A) to store the material therein, and (e) repeating the steps (c) and (d), the obtained injection-molded product is free from uneven properties and can exhibit a good quality. The present invention has been attained on the basis of this finding.
It is an object of the present invention to provide an improved injection molding process and injection molding machine, wherein the kneading can be stably conducted without being adversely affected by the feed pressure from the reservoir devices.
It is an another object of the present invention to provide an improved injection molding process and injection molding machine, wherein it is possible to obtain an injection-molded product which is free from uneven properties and can exhibit a good quality.
To accomplish the aims, in a first aspect of the present invention, there is provided a process for injection-molding a composite resin composition, comprising:
(a) kneading particles and a binder resin using a kneader;
(b) feeding the obtained kneaded material to one (A) of two reservoir devices to store the material therein;
(c) feeding the kneaded material stored in the reservoir device (A) to an injection device wherein the kneaded material is then injection-molded, and simultaneously feeding the kneaded material from the kneader to another reservoir device (B) to store the material therein;
(d) feeding the kneaded material stored in the reservoir device (B) to the injection device wherein the kneaded material is then injection-molded, and simultaneously feeding the kneaded material from the kneader to said one reservoir device (A) to store the material therein; and
(e) repeating the steps (c) and (d).
In a second aspect of the present invention, there is provided an injection-molding machine comprising:
a kneader for kneading particles with a binder resin;
a pair of reservoir devices (A) and (B) for temporarily storing the kneaded material supplied from the kneader;
an injection device for injection-molding the kneaded material, the kneaded materials temporarily stored in the reservoir devices (A) and (B) being alternately fed to the injection device;
a reservoir switching means connected between the kneader and the pair of reservoir devices (A) and (B), which are switchable for alternately storing the kneaded material in the reservoir devices (A) and (B); and
a feed switching means connected between the pair of reservoir devices (A) and (B) and the injection device, which are switchable for alternately feeding the kneaded material from the reservoir devices (A) and (B) to the injection device.
In a third aspect of the present invention, there is provided an injection molded product comprising particles and a binder resin, produced by a process comprising:
(a) kneading particles and a binder resin using a kneader;
(b) feeding the obtained kneaded material to one (A) of two reservoir devices to store the material therein;
(c) feeding the kneaded material stored in the reservoir device (A) to an injection device wherein the kneaded material is then injection-molded, and simultaneously feeding the kneaded material from the kneader to another reservoir device (B) to store the material therein;
(d) feeding the kneaded material stored in the reservoir device (B) to the injection device wherein the kneaded material is then injection-molded, and simultaneously feeding the kneaded material from the kneader to said one reservoir device (A) to store the material therein; and
(e) repeating the steps (c) and (d).